As an example of electronic equipment having a receiving device that receives a high frequency input signal, a television receiver can be mentioned. The television receiver includes a receiving device that receives a high frequency input signal through an antenna.
In a conventional receiving device, a so-called heterodyne system is employed as shown in FIG. 11.
In the heterodyne system as shown in FIG. 11, a high frequency input signal f is input to an antenna 1000. The high frequency input signal f is mixed with a mixing frequency f1 to be selected, so that the intermediate frequency (f−f1) is obtained. Further, after passing through a filter or the like, the intermediate frequency (f−f1) is mixed with a constant frequency f2, and a base band signal ((f−f1)−f2) is obtained. This base band frequency has a range of DC (direct current) to several ten MHz.
Note that in this case the relation between f, f1 and f2 is f=f1+f2.
However, the heterodyne system mentioned above requires a large number of components and frequency conversion of many times, which results in a high cost.
Then, as shown in FIG. 12, a direct conversion system having a small number of components and a simple structure is beginning to be used. In the direct conversion system, when a high frequency input signal f is input to an antenna 1010, the mixing frequency f1 which is the same as the selection frequency is mixed with the high frequency input signal, and the differential signal is taken out to obtain (f−f1) as a base band signal.
Note that, in this case, the relationship between f and f1 is f=f1.
In such a receiving device, as shown in FIG. 13, an amplifier 1020, a filter 1024, a direct conversion unit 1026 and a digital demodulator 1028 are formed on a substrate 1016. A shield case 1030 and a shield cover 1040 are detachably loaded onto the substrate 1016, and the shield case 1030 and shield cover 1040 shield each elements on the substrate 1016 from high frequency waves.
The shield cover 1040 is engaged with ribs 1061 in the shield case 1030, using a plurality of claws 1060 on the peripheral portion thereof to be hooked, and the shield cover 1040 and shield case 1030 are contacted and fixed to each other.
The shield case 1030 has a frame 1055, and an inner partition plate 1056 is disposed in the center of the frame 1055. The frame 1055 has a plurality of claws 1050, and when the claws 1050 are fixed into concave portions 1017 in the substrate 1016, the shield case 1030 is fixed to the substrate 1016.
With the above structure, the amplifier 1020, the filter 1024, the direct conversion unit 1026 and the digital demodulator 1028, each of which is a functional block of the substrate 1016, are surrounded and shielded.
The inner partition plate 1056 of the shield case 1030 is, for example, disposed to shield between the filter 1024 and the direct conversion unit 1026, where the partition plate 1056 is soldered to the ground of the substrate 1016 to function as a shield plate.